1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing an object to be polished (substrate) such as a semiconductor wafer to a flat mirror finish.
2. Description of the Related Art
As semiconductor devices have become more highly integrated in recent years, circuit interconnections have become finer and distances between these circuit interconnections become smaller. In the case of photolithography which can form interconnections that are at most 0.5 μm wide, it is required that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because the depth of focus of an optical system is relatively small. As a means for planarizing a surface of a semiconductor wafer, a polishing apparatus for performing chemical mechanical polishing (CMP) has been known.
This type of polishing apparatus includes a polishing table having a polishing pad thereon, and a polishing head having a top ring. An object to be polished such as a semiconductor wafer is placed between the polishing table and the top ring. While a polishing liquid (slurry) is being supplied to a polishing surface (surface) of the polishing pad, the object to be polished is pressed against the polishing surface of the polishing pad by the top ring to polish the object to a flat mirror finish.
When the object to be polished is polished, abrasive particles and polishing debris are attached to the polishing surface of the polishing pad, resulting in a change in properties of the polishing pad and deterioration in polishing performance. Therefore, as the objects to be polished are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, in order to regenerate the polishing surface of the polishing pad, the polishing apparatus generally has a dresser head having a dresser disposed adjacent to the polishing table for dressing the polishing pad.
If such polishing apparatus is used in a corrosive atmosphere of chemicals, then a gas of the chemicals enters a cover for enclosing components of the polishing head through clearances in the cover, thereby tending to corrode the components of the polishing head that are made of aluminum, stainless steel, steel, or the like. This holds true for the dresser head having the dresser. The gas of the chemicals also enters a cover for enclosing components of the dresser head, thereby tending to corrode the components of the dresser head.
Further, in a polishing apparatus having an electropneumatic regulator for a top ring, a high-temperature gas of chemicals enters a cover for enclosing the electropneumatic regulator for the top ring, or the temperature inside the cover rises due to the heat from a driving unit such as a top ring rotating motor, causing the electropneumatic regulator for the top ring to suffer temperature drifts which are likely to develop pressure variations in the pneumatic pressure.
There has been proposed a polishing apparatus having a polishing head rotating means for rotating a polishing head (top ring), and the polishing head rotating means is disposed in a hermetically enclosed state, preferably in a positively exhausted state for air circulation to reduce an amount of dust (particles) discharged from the polishing apparatus into ambient atmosphere, as disclosed in Japanese patent No. 3043578. Further, the applicant of the present application has proposed a polishing apparatus including a substrate holding mechanism (polishing head) and a polishing table which are covered by a capsule assembly, and a purge mechanism for introducing, when necessary, a purge gas into a top ring capsule that houses the substrate holding mechanism, in order to prevent a gas generated from a corrosive and toxic processing liquid from being scattered around in the polishing apparatus, as disclosed in Japanese laid-open patent publication No. 2008-166709.